1. Field of the Invention
The present invention relates to a method of manufacturing an amorphous magnetic alloy and, more particularly, to a method of manufacturing an amorphous magnetic alloy having a high permeability and a high saturated magnetic flux, which is suitable as a soft magnetic core material for magnetic heads or the like.
2. Brief Description of the Prior Art
Amorphous alloys known to be employed as soft magnetic core materials are of the Fe type, the Co-Fe type, the Co-Fe-Ni type, and the Fe-Ni type. Those amorphous alloys are manufactured by the centrifugal quenching method, the single roll method or the double roll method. In instances where those amorphous alloys are employed for magnetic heads, a high permeability in a low frequency range is required. Those manufacturing methods as mentioned hereinabove, however, produce an internal stress .sigma. in the amorphous ribbon during the manufacturing steps and the internal stress, when associated with the magnetostriction .lambda., deteriorates the magnetic performance, particularly the permeability .mu.(.mu..varies.1/.lambda..sigma.). It is well known that, in an instance where the amorphous alloy of the Fe type is employed, the internal stress produced during the manufacturing step can be reduced by means of the annealing in the magnetic field or in no magnetic field after the manufacture, whereby the permeability is improved. However, a deterioration of permeability with a striction that will be produced through the punching of the amorphous alloy ribbon into core forms after the annealing or through the etching step cannot be prevented to a satisfactory extent by conventional methods.
It was already found in Japanese Patent Early Publication No.80,303/1980 that the amorphous alloy of the Co-Fe type can permit a great improvement in permeability by the rapid quenching after maintenance at a temperature T higher than the Curie temperature Tc and lower than the crystallization temperature Tcry (0.95.times.Tc.ltoreq.T.ltoreq.Tcry). Recent commercialization of magnetic recording media in which magnetizable or magnetic metal particles or powder having a high coercive force are employed, however, requires the employment of an amorphous alloy possessing a high saturated magnetic flux Bs, for example, higher than about 8,000 Gauss in addition to a high permeability. To render the saturated magnetic flux of the amorphous alloy higher, it is necessary to increase the amount of a transition metal element such as Co, Fe, Ni or the like to be contained in the alloy; however, an increase in the amount of the transition metal element to be added thereto provides a general tendency to decrease the Curie temperature Tc and at the same time increase the crystallization temperature Tcry of the amorphous alloy. For example, where the total amounts of Co and Fe in the amorphous alloy of the Co-Fe-Si-B type exceeds 78 at %, the crystallization temperature Tcry is lowered than the Curie temperature Tc. This results in the fact that, in instances where the amount of the transition metal element is increased in order to highten the saturated magnetic flux and the amount of the transition metal element exceeds a particular limit, for example, 78 at % in the case of the Co-Fe-Si-B type amorphous alloy, it becomes impossible to apply a method of improving the permeability by quenching from a temperature higher than the Curie temperature as hereinabove set forth. Further, particularly the Co-Fe type alloy has a large induced magnetic anisotropy resulting from the Co component present in the alloy so that, even if the alloy having a high saturated magnetic flux would have been produced, it cannot be practically employed without any treatment because of its low permeability.
We have already proposed in our copending U.S. Pat. Application Ser. No.161,077 (U.S. Pat. No. 4,379,004) that the heat treatment or annealing is carried out at a temperature lower than the crystallization temperature while relatively rotating an amorphous alloy material in a static magnetic field or in a rotating magnetic field. This method permits a disappearance of the induced magnetic anisotropy in the amorphous alloy and provides a great improvement in the permeability. It is further to be noted that, as this method is not dependent upon the relation of the Curie temperature Tc with the crystallization temperature Tcry of the amorphous alloy, it can be applied to a wide range of amorphous alloys. This method, however, requires that the heat treatment or annealing be carried out at such a state that the velocity of varying a magnetic field is rendered greater than the average velocity at which the alloy atoms are transferred by means of heat so that a relatively large rotating velocity is required.